JPS6118902A - Manufacture of dyestuff polarizing film - Google Patents

Abstract

PURPOSE:To improve the durability, polarization degree, and single substance transmissivity of the dyestuff polarizing film by treating a high polymer film in which a dichroic dye is adsorbed and oriented with a solution containing boric acid and forming the dyestuff polarizing film. CONSTITUTION:The high polymer film in which the dichroic dye is adsorbed and oriented is treated at 30-80 deg.C, preferably, 50-75 deg.C with the solution containing, for example, 1-15wt%, preferably, 5-10wt% boric acid to form the dyestuff polarizing film. An azo dye shown by a formula I, anthraquinone dye shown by a formula II, etc., are usable as the dichroic dye. When a film formed of polyvinyl alcohol and its derivative is used as the high polymer film, the adsorption and orientation are facilitated and the effect of the boric acid treatment is large. The dichroic dye is oriented by orienting an adsorbent or the film later.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a dye-based polarizing film, which comprises treating a polymer film on which a dichroic dye has been adsorbed and oriented with an aqueous solution containing boric acid. By treating with an aqueous solution containing boric acid, the single transmittance (light transmittance of one polarizing film) and degree of polarization are improved compared to untreated ones.

Currently, polarizing films are generally produced by adsorbing iodine or dichroic dyes as polarizing elements onto stretched and oriented polyvinyl alcohol or its derivatives.

Among these, polarizing films that use iodine as a polarizing element have excellent initial polarization performance, but are weak against water and heat, and have problems with their durability when used for long periods in high temperature and high humidity conditions. There is. In order to improve durability, methods have been considered such as strengthening the treatment with an aqueous solution containing formalin or boric acid, or using a polymer film with low moisture permeability as a protective film, but Durability is insufficient in this condition.

Although it has durability against water and heat, it has the disadvantage of poor polarization performance.

In view of these circumstances, the inventors of the present invention have conducted extensive studies with the aim of improving the polarizing performance of polarizing films that use dichroic dyes as polarizing elements, and have developed a polymer film that adsorbs and orients dichroic dyes. discovered that a method of treatment with an aqueous solution containing boric acid was effective, and developed the present invention.

That is, the present invention relates to a method for producing a dye-based polarizing film, which comprises treating a polymer film on which a dichroic dye has been adsorbed and oriented with an aqueous solution containing boric acid.

The purpose is to provide a dye-based polarizing film that has excellent durability, a high degree of polarization, and a high intermediate transmittance.

Polymer films used in the present invention include polyvinyl alcohol and its derivatives, those modified with olefins such as ethylene and propylene, crotonic acid, acrylic acid, methacrylic acid, maleic acid, etc., EVA resin (ethylene-vinyl acetate resin) , saponified EvA resin, nylon resin, polyester resin, etc. are used. Among these, films made of polyvinyl alcohol and its derivatives are particularly useful polymer films for the present invention because dyes are easily adsorbed and oriented and the effect of boric acid treatment is large.

Boric acid concentration is 1-15%, preferably 5-10%
, and the treatment temperature is 30 to 80°C, preferably 50°C.
Preferably, the temperature is in the range of ~75°C. If the boric acid concentration is 1% or less and the temperature is 30°C or less, the treatment effect will be small, and if the boric acid concentration is 15% or more and the temperature is 80°C or less, the polarizing film will become brittle, which is not preferable.

Further, the dye used in the present invention may be any dye as long as it has a high dichroic ratio, and generally water-soluble direct dyes are used.

Azo dyes represented by the general formula:

When these direct dyes are used, dye adsorption and
Orientation can be achieved by conventional means. Orientation of the dichroic dye adsorbed onto the polymeric film is achieved by orienting the film before or after adsorption.

The film made of polyvinyl alcohol or its derivatives may be stretched by either a wet force method or a dry compression stretching method.

The boric acid treatment can be carried out after dye molecules are adsorbed and oriented on polyvinyl alcohol or its derivatives. Furthermore, if necessary, fixing treatment may be performed in combination with an aqueous solution containing a cationic polymer compound.

The dye-based polarizing film thus obtained has the characteristics of a higher single transmittance and a higher degree of polarization than conventional films, and therefore can be used for liquid crystal display applications.

It is particularly suitable for applications that require high durability, such as in-vehicle applications and display applications for various industrial instruments.

The present invention will be explained in more detail with reference to Examples below, but these are merely illustrative and are not intended to be limiting.

In addition, the degree of polarization in the present invention refers to preparing two polarizing films or polarizing plates and measuring the light transmittance curve with the two polarizing plates superimposed. Measuring device: Shimadzu UV-2) 0
spectrophotometer), and is the value determined by the following formula.

Here, H1□ is a value (called parallel transmittance) measured when two samples are stacked so that the polarizing films are aligned in the same direction.
l is a value (referred to as 111 cross transmittance) measured when two samples are superimposed so that the orientation directions of the polarizing films are orthogonal to each other.

Example 1 A polyvinyl alcohol film (Kurare Vin'#7500) having a thickness of 75 μm was stretched 4 times along the vertical axis to obtain a polarizing film base material. While keeping this PVA film under tension, dye (Japanol Fast Black)
D.

Taoka Chemical Industry Co., Ltd.) 0.02wt%, anhydrous sodium sulfate Q, 5w
It was immersed for 40 minutes in an aqueous solution at 50°C consisting of t%. Furthermore, after 5 minutes of immersion in a 65° C. aqueous solution containing 7.5 wt % of Hou, the film was washed with 20° C. water for 80 minutes to obtain a polarizing film. The single transmittance and degree of polarization of this polarizing film are shown in FIGS. 1-1 and 1-2.

Comparative Example 1 A polarizing film was manufactured under the same conditions as in Example 1 except that no boric acid treatment was performed. The single transmittance and degree of polarization of this polarizing film are also shown in FIGS. 1-1 and 1-2. Compared to Example 1, the single transmittance and degree of polarization are lower.

Example 2 While keeping the same polarizing film base material as in Example 1 under tension,
8 types of dyes (Direct 5kyBlue 6B
, Birect Dark Green BA.

Sumilight Red 4B, both manufactured by Sumitomo Chemical Co., Ltd.), respectively, at o, o o g wt%, 0.0
15wt%, 0.009wt%, anhydrous mirabilite 0.2wt
% in an aqueous solution at 50°C for 40 minutes. Furthermore, after being immersed in an aqueous solution of 7.5 wt% boric acid at 66°C for 5 minutes, the film was washed with water at 20°C for 80 seconds to obtain a polarizing film. Figure 2-1 shows the single transmittance and degree of polarization of this polarizing film.
and -2.

Comparative Example 2 A polarizing film was manufactured under the same conditions as in 1. The single transmittance and degree of polarization of this polarizing film are also shown in FIGS. 2-1 and 2-2.

Compared to Example I, the single transmittance and degree of polarization are lower.

Reference Example Commercially available cellulose) IJ 7 acetate film (8
0μ, manufactured by Fuji Photo Film Co., Ltd.) was bonded using a urethane adhesive.

After measuring the initial polarization performance of the polarizing plate thus obtained, it was left in a constant temperature and humidity chamber at 85° C. and 90% RH for 200 hours. The polarization performance after the test was measured, and it was exactly the same as the initial performance, with no change.

[Brief explanation of the drawing]

1-1 and 1-2 are wavelength-unit transmittance and wavelength-polarization degree relationship diagrams of the polarizing films produced by the methods of Example 1 and Comparative Example 1, respectively. 2-1 and 2-2 are wavelength-single transmittance and wavelength-polarization degree relationship diagrams of the polarizing films produced by the methods of Example 2 and Comparative Example 2, respectively. -IO complete- Wavelength (nm) Figure 1-1 Wavelength (nm) Wavelength (nm) Figure 2-1 Wavelength (nm)

Claims (2)

[Claims] (1) A method for producing a dye-based polarizing film, which comprises treating a polymer film on which a dichroic dye has been adsorbed and oriented with an aqueous solution containing boric acid. (2) The method according to claim 1, wherein the polymer film is a film made of polyvinyl alcohol or a derivative thereof.